it's nothing special, temp sensor is located in closed case additionally heated up by continuous solar charging. if you want to have real measurements you have to buy external sensor such as tempe.
Not one Garmin Edge that I have owned has ever shown an accurate temperature. They have all been high by several degrees Fahrenheit, or a couple of degrees Celcius. I started with the Edge 705, went to the 800, 1000, 1030, 1030 Plus, and now the 1040 non-solar.
In addition to sunlight heating up the case and thereby increasing the temperature sensor inside the case, I also found that running an external battery (small power block with a cord) also raises the internal temperature due to charging the battery during an active ride. At coffee breaks, I try to park my bike in the shade or cover my Edge unit with my helmet to keep direct sunlight off of it. Several of us in our club use the WindField Garmin IQ app (and use the Pro version - $12 per year and well worth it). I have secondary values for "Feels like", Humidity, UV Index, Gusts, Distance from Weather Station, and Last Update (time). These are my settings, but there are other choices for the secondary values. I use WeatherKit for my weather data source and find it more accurate than Accuweather, Nearest (wx station), and others. You could select Temperature instead of "Feels like", which factors in humidity and wind chill. The data will be input from the source of your selection. I don't trust "Nearest" since backyard wx stations are not always maintained or located in the good spots. I've been using WindField for several years. You can watch a recent YouTube video by GP Lama to see a demo.
